Trite? Maybe, but no less true. Marc Andreessen, of the venture firm Andreessen Horowitz (which funds three companies on the list), says that software is “eating the world.” Well, it’s definitely eating our list. With the help of CB Insights, a New York data firm, we produced a ranking of privately held, high-growth American companies that’s dominated by those who make money by churning out code. We filed 48 of the top 100, and five of the top ten, under the Software & Services industry.

3Cinteractive, our top pick for 2013, is a prime example. Founded by three former sales reps at MCI, the company has found explosive growth, and hefty margins, making software that helps consumer giants connect with their customers en masse via mobile phones. That text reminding you to pick up a prescription from the pharmacy? 3Ci makes it happen, along with countless other interactions for clients like Walgreens, and . In a world where phones now outnumber people, we think 3Ci is set up enviably in an enormous, rapidly expanding market.

Even companies slated under traditional industries on our list, like finance or retail, are finding their niches by applying technology to long stagnant business models. , our No. 2 pick, raked in half a billion in sales last year using the Internet to provide subprime borrowers with loans. Try reaching that kind of scale, that quickly, with a brick-and-mortar bank.

In the retail sector, Wayfair, at No. 16, presents a similar case study. The company sold $600 million worth of home décor products last year, all through one massive online portal. Even a Costco-sized floor plan couldn’t handle their inventory of five million different items.

In the face of tech's domination, we did find some traditional companies with bright prospects. While No. 5 Popchips differentiates itself among snack brands with a unique product and a celebrity-heavy marketing strategy, the company sells chips the old-fashioned way—through grocery outlets and convenience stores—just as Henry Lay did 80 years earlier.

Thankfully for Anytime Fitness, exercise is still one activity that can’t be outsourced to software. The chain of franchised gyms spans 14 countries. As No. 14 on our list, the company notched steady growth even as sales climbed to nine digits. Revenues approached $500 million last year, nearly double the company's 2009 take.

Methodology

To produce our Most Promising list, we started with the premise that one metric—like revenue or valuation—doesn't say much about a company’s overall health. Instead we strove for a holistic gauge, trying to pin down companies' trajectories by looking at a slew of variables. Over the course of six months we reviewed thousands of applications from businesses across the country. The final assessment is based on growth (both in sales and hiring), quality of management team and investors, margins, market size and key partnerships. We turned to CB Insights, which specializes in assessing private companies for hedge funds and venture capital firms, to refine our search. Their Mosaic software, developed with the help of $650,000 in grants from the National Science Foundation, scans 45,000 digital sources to measure a company’s health. A new distribution deal, for example, marks a positive signal, while the loss of an executive is a negative. Mosaic gathers those myriad signals into a score that FORBES uses as an initial guide in producing the list. After verifying sales numbers, speaking with each company and debating their merits and blemishes, we end up with the final ranking.

Ranking private companies, especially outfits as strong as those on our list, is never easy. But watching the race play out in the real world is always fascinating.